1. Field of the Invention
This invention relates to conveyor drives and particularly to magnetic drives for endless, woven magnetically attractable conveyor belts and the like in high traction force systems.
2. Description of the Prior Art
In glassware manufacturing it is known to utilize an endless, woven, metallic conveyor belt of, for example, ferrous metal wire mesh construction for transferring glassware between a forming machine and an annealing lehr, for example. There are also inumerable other industries and manufacturers where articles are transferred from one location to another by endless, woven metallic wire mesh conveyor belts. Further, there are many different techniques and machines for driving the conveyor belts including pulley drives, tractor drives and magnetic drives. The problems encountered with known metallic wire mesh conveyor belt drives are numerous: for example, after use for a period of time, the belt tends to stretch; this causes the belt to slip as it is being driven. Slippage of the belt is undesirable because it is an inefficiency in the conveyor system; it is also very undesirable where the conveyor is utilized to transfer articles in some sort of timed relationship with other processes being performed on the articles because it causes the articles to get out of spatial relation. For example, in glassware manufacture, it is desirable to transport hot newly formed glassware from the forming machine to an annealing lehr; it is essential that the belt be driven at a constant critical speed to provide for known equal spacing of the glassware placed thereon as the conveyor belt passes the multiple sections of the composite glassware forming machine. If the belt slips, the articles are no longer equally spaced.
Pulley drives depend entirely on friction between the belt and the pulley wheel. As the belt wears it stretches requiring constant adjustment of belt tension. Lagged pulleys, pulley wheels having a friction increasing material applied thereto, show some improvement over the plain pulley, but not a significant improvement. Tractor drives, such as the drive shown and described in U.S. Pat. No. 3,249,209, utilize friction and compression of the belt to pull it. The tractor drive is a complex machine and costly because of the complexity; further, it is somewhat prone to failure because of the complexity and great number of parts which form it. The magnetic tractor drive shown in U.S. Pat. No. 3,497,056 relies completely on the shear force of the magnets to drive the conveyor belt. There is no utilization of friction forces or wrap forces to drive the belt. Other magnetic drives known in the art, such as drive wheels having magnets therein, also rely only upon magnetic shear force to drive the belt. Further, known magnetic drive wheels have the poles of the magnet disposed substantially parallel to the direction traversed by the belt; this causes poor holding of the belt by the magnetic wheel at the belt edges since the magnet's force is applied mostly to the center of the belt, with very little force holding the edge of the belt.
Our invention overcomes these and other deficiencies in conveyor belt drives.